Breastfeeding is highly protective against bacterial diarrhea, a major cause of morbidity and mortality in children. Our overallgoal is to identify secretor human milk glycans that can act as novel prophylactic/therapeutic agents against diarrhea, especially bacterial diarrhea. Weidentified human milk oligosaccharides, and especially a1,2-fucosyl (secretor) oligosaccharides, that inhibit a large family of pathogens. Secretor oligosaccharides bind to adhesins of enteropathogens, inhibiting their binding to cell surface glycans of the gastrointestinal tract. We also find that human milk high molecular weight (HMW) glycoproteins that contain secretor moieties bind strongly to pathogens, and seem to have higher affinity and more specificity in their inhibition of pathogens than oligosaccharides.This project will study binding characteristics of these HMW human milk glycans to determine their structure/function relationships, and dentify those with the highest efficacy. This will allow rational design of a new generation of synthetic human milk glycans that optimize inhibition of pathogen binding. This project will continue to produce 2'- fucosyllactose (2'-FL) the synthetic secretor human milk oligosaccharideanalog that we developed in our aboratory, and will test this product, in preclinical studies, for safety and efficacy. This project will further examine the increased burden of diarrhea! disease in secretor relative to non-secretor infants, and the reduced burden of disease obtained by consumption of secretor glycans in human milk. Thus, the specific aims are: 1) Identify, isolate and characterize HMW secretor glycoproteinsthat bind to bacterial enteric pathogens and determine the contributions of glycosylation patternsto the strength of inhibition. 2) Synthesize an a1,2-fucosylglycan in bacteria, and test its safety and efficacy in animal models. 3) Test the secretor phenotypes of infants and maternal milk in a cohort of breastfeeding children 0 - 2 years of age as determinants of infant risk of all diarrhea and bacterial diarrhea. The data obtained will extend our understanding of infant gut and human milk glycans in the innate defense of the neonate. This will ultimately translate into testing our prototype synthetic human milk glycan as a novel prophylactic or therapeutic agent, into generating a second generation synthetic glycan, as well as a novel biomarker for prediction of risk of diarrhea. RELEVANCE (See instructions): The research proposed in this application is designed to transform our fundamental understanding of human milk glycans as agents that prevent risk of bacterial causes of diarrhea and to translate our discoveries into new medications, food substances, and diagnostic tools that promote the health and survival of infants and children worldwide